Interactions between T lymphocytes and antigen presenting cells involve adhesion molecules that are also implicated as regulators of cell activation. Recently, the investigators have shown that the CD59 antigen is a second ligand for CD2 on T cells in addition to the well recognized interaction with CD58 (LFA-3). The interactions among these cell surface antigens are very central to immune regulation and will likely form the first paradigm for understanding adhesion molecule interactions. The CD59 is also an important regulator of the formation of the complement membrane attack complex. Definition of the significant factors in this interaction will be accomplished initially with molecular studies. Site- directed mutagenesis will be performed on cDNAs encoding both the CD59 and CD58 antigens. The mutants will be screened using monoclonal antibodies, adhesion assays and for complement function in the case of CD59. Subsequently, the immunogenicity of these antigens will be examined after transfection into several sources of antigen presenting cells. Recombinant protein will be generated from CHO transfectants or baculovirus expression systems and used for determination of the three dimensional structure. These antigens as well as MHC class II antigens may contribute to the immunogenicity of endothelial cells. The immunogenicity of porcine endothelial cells transfected with CD58, CD59 and/or human MHC class II will be initially evaluated in vitro. These transfected cells will also be utilized to determine whether porcine cells could be a potential source for xenotransplantation into human. A model murine system in which the immune system of SCID mice has been reconstructed with human cells will be employed. The immunogenic properties of modified porcine endothelial cells will be evlauated after introduction in synthetic vascular networks. This approach should also provide insight into immune-mediated injury.